The present invention relates to a method of providing an internal combustion engine of the kind comprising at least one power cylinder which includes a working chamber with a volume variable by the displacement within the cylinder of a piston between a top dead center position and a bottom dead center position under the effect of pressure forces periodically generated within said chamber whereas with each cylinder are associated intake and exhaust means for a gaseous fluid, the piston of each cylinder being connected to a crankshaft of the engine, as well as an engine for carrying out this method.
The known engines of this type make use of either a two-stroke or a four-stroke thermodynamic cycle. In a four-cycle engine the cylinder is filled with an air-fuel mixture when the piston is near its bottom dead center. Then while moving forward the piston would compress this mixture and the fuel would vaporize under the rise of the temperature. When the piston arrives near its top dead center an ignition plug would ignite the mixture by means of a spark thereby inducing a sudden elevation in temperature and in pressure. When moving backwards the piston allows the combustion gases to expand and it is at this time that a usable work is produced. When it arrives near its bottom dead center the gases are discharged through an exhaust valve arranged in the cylinder head in view of a so-called longitudinal scavenging or through exhaust ports formed in the cylinder liner, sleeve or barrel and uncovered by the piston owing to a so-called cross-flow scavenging. The residual gases are then scavenged or swept out by the incoming flow of the fresh air-fuel mixture which is fed through scavenging ports formed at the lower portion of the cylinder liner, sleeve or barrel and uncovered by the piston a little later than the exhaust ports. Both cycles therefore are the compression and the expansion.
The four cycle Diesel engine makes use of a comparable principle where the difference consists in the manner of introducing the fuel which in this case is directly injected into the compressed hence hot air and would then ignite spontaneously.
In both cases the energy output efficiency would depend among other factors from the volumetric compression ratio. The higher the compression ratio, the higher the efficiency. Now this compression ratio is limited in the case of an engine operating with gasoline by the risk of premature hammering or preknocking of the mixture and in the case of a Diesel engine among other factors by the necessity of preserving a suitable combustion chamber. In any case with a thermodynamic cycle such as described hereinabove, the increase in output efficiency becomes weaker and weaker for an equal increase in the compression ratio from a value of 10 to 15 of the latter and in the case of a Diesel engine there mainly are the mechanical stresses which would determine the critical volumetric compression ratio.
The output efficiency of the two-stroke cycle with controlled ignition generally is lower than that of the four-stroke cycle since a fuel loss is unavoidable during the scavenging of the combustion gases by the fresh air-fuel mixture. Another defect of the two-stroke cycle with controlled ignition as compared with that of a four-stroke cycle is the bad operation under partial load wherein a throttling at the suction would result in a greater dilution of the fresh charge by the combustion gases during the scavenging which may therefore make the combustion difficult.
The main object of the present invention is to increase the power efficiency of the two-cycle internal combustion engine with reciprocating pistons of the kind defined hereinabove.
To reach this goal the method according to the invention is characterized in that it consists in using at least one cylinder operating as a low pressure two-stroke cylinder and two cylinders operating as combustive cylinders, in that at each stroke of the piston of the low pressure cylinder towards its top dead center the gaseous fluid let thereinto is alternately discharged into one of the two combustive cylinders, in that the latter is caused to then successively perform an intake stroke for admitting the fluid to which fuel has been added, a stroke for compressing the air-fuel mixture, a stroke of a first expansion of the combustible gases after the ignition of the fluid and a stroke of discharging the combustible gases into the low pressure cylinder during the second expansion stroke thereof following that of said discharge of fresh air with a view to perform a second expansion of the combustible gases and their exhaust from the engine.
The engine for putting this process into practice is characterized in that the pistons of the low pressure and combustive cylinders, respectively, are connected to the crankshaft so that the pistons of the combustive cylinders on the one hand and the piston of the low pressure cylinder on the other hand would move in opposite directions, the low pressure working chamber is likely to communicate with a gaseous fluid intake way and with a combustible gases exhaust way and with the working chamber of each combustive cylinder on the one hand through a way for discharging fresh air into this working chamber through the agency of a discharge valve associated with the low pressure cylinder and of an inlet valve associated with the combustive cylinder and on the other hand through a way for transferring the combustible gases through the medium of a transfer valve associated with the combustive cylinder and in that the valves are operated so that said discharge valve be open during the stroke of the piston of the low pressure cylinder towards its top dead center at the same time as and in alternating relationship with the inlet valve of one of the two combustive cylinders and in that the transfer valve of a combustive cylinder is open during the second stroke of the piston of the low pressure cylinder towards its bottom dead center after the intake of the gaseous fluid into this cylinder.